This invention relates to a metal vapor laser capable of cold operation, or operation at low temperatures. The laser holds promise for use as a light source with apparatus that use high-power lasers, among which a dye laser apparatus for isotope separation, a vapor deposition apparatus that depends on laser ablation and a laser-dependent metal processing machine are worth particular mention.
Thus, the present invention relates to a metal vapor laser that can be operated at much lower temperatures than the conventional high-temperature version which produces metal vapors by thermal evaporation; because of its cold working environment, the laser of the present invention experiences smaller degradation of laser power due to temperature while undergoing limited thermal damage to its structural components; as a result, laser light can be oscillated to produce high output power and, at the same time, the warmup time can be shortened significantly.
Metal vapors for use in metal vapor lasers have heretofore been generated at either high or low temperature. In the first case, the interior of a laser tube is maintained at high temperature (e.g., about 1500.degree. C. in the case of copper vaporization) by either discharge or electric heating so as to generate metal vapors. However, this approach has had several drawbacks such as, thermal deterioration of structural components by high temperature and the long warmup time to laser oscillation.
In the second case, there is the need to synthesize a rare gas, or a metal halide gas, which is directly used as a laser medium; in addition, the metal halide gas is decomposed to release the metal for laser oscillation but the laser thus produced does not have satisfactory power.
To raise the temperature in the laser tube to a sufficiently high level to produce metal vapors, a heat insulator or the like is used so that the heat resulting from discharge is accumulated in the tube to heat the metal or, alternatively, tile metal is directly heated with an oven in the laser tube. In either way, the method suffers from the disadvantage that an expensive heat insulator and ceramic tube that can withstand elevated temperatures have to be used in order to maintain a high temperature within the laser tube and, what is more, the need to cool those parts adds considerably to the complexity of the overall system. Another problem with raising the temperature in the laser tube is that population rate of lower energy levels of electron for laser oscillation by the atoms of metal vapors are thermally increased and the probability for population inversion decreases to lower the efficiency of laser oscillation. As is well known, laser oscillation utilizes that is generated when the energy state of an atom emission makes transition from a higher level to a lower level. At elevated temperatures, the proportion of atoms In the lower energy state will increase so much as to reduce the probability for population inversion (i.e., the condition in which the higher energy levels are more populated than the lower levels).
As a further problem, the method takes so much time to produce the desired temperature that as many as 1 to 2 hours are necessary to achieve laser oscillation. If a heater is to be used, it must be deliverately installed within the laser tube for producing metal vapors and a puddle of metal has to be heated as if it were in an oven. This also adds to the complexity of the system and yet it is difficult to produce the metal vapors uniformly within the laser tube.
As already mentioned, the second approach using a metal halide gas has suffered from disadvantages such as the need to prepare a special gas and low output power due to the low efficiency. To solve this problem, it has been necessary to perform the following special technique:
a hydrogen halide is introduced into a laser discharge tube, in which pure metal is settled and a metal halide compound is generated as a metal halide gas is evaporated while, at the same time, the metal halide vapor is composed by discharge to generate metallic atoms which will serve as a laser medium.